Characterization of Structure of Porous Materials by Ultrasonic Reflectometry

The paper addresses experimental and modeling issues related to application of air coupled ultrasonic reflectometry for studies of structure of porous materials. The structure of the materials is characterized by porosity, permeability and tortuosity. Among experimental problems role of finite beam effect, precision of sample positioning and fluctuations of ultrasound in air are considered. Theoretical issues concern selection of proper model used for identification of parameters of structure of the materials which may or not incorporate dissipation of waves, deformation of skeleton, as well as different forms of boundary conditions. Predictions of models assuming stiff and deformable skeleton are compared for selection of appropriate tool for reflectometry in air. Role of specular and diffusive components of reflected wave are discussed. Materials with broad range of porosity and permeability are taken into account.